The need to reinforce rubber materials with metal has been recognised for some time, and there are many instances wherein metal is embedded in rubber for stiffening purposes and in certain instances the metal is perforated so that the rubber is integral through the perforations in the metal as well as being adhered to the metal surface. It is well recognised that it is difficult to achieve a very strong adhesion between rubber and metal by "lay up" methods, and such products have therefore usually been formed by moulding the rubber on or around the metal under conditions of high pressure.
It is not feasible to mould a large sheet over a metal grid since the grid will need support within the moulding die and therefore will not be fully encased, so that the metal will be liable to acid or abrasion attack if the sheet is used, for example, for the lining of acid tanks, pipes used in mining operations and the like. In the alternative, if the rubber is merely cemented to a metal sheet, there is a danger of the rubber tearing away due to poor adhesion or the metal being subject to abrasion or chemical attack. Known adhesives usually achieve only about a 40 percent adhesion, and this diminishes above temperatures of about 70.degree.C.
It will be recognised by those skilled in the art that the possible alternatives of utilising woven mesh, sheet metal having a large number of small perforations therein, or expanded metal for the reinforcement of rubber sheets are all subject to certain disabilities. Woven mesh and expanded metal include recesses into which the rubber is not readily deformed, and even if a moulding technique were to be utilised, there is a danger of air pockets being formed between the metal and the rubber, and these constitute weaknesses which can result in tearing of the rubber. If perforate sheet metal is used in a lay up process, the adhesion between the rubber and the imperforate portions of the metal is likely to be poor, and the area wherein the rubber penetrates through the apertures is likely to be ineffective in providing sufficient adhesion to a backing sheet (if used) to overcome the difficulty of poor adhesion to the metal. If the perforations in a sheet metal plate are increased in size to the extent that adhesion to a backing sheet becomes of significance, then there is a considerable wastage of metal from the perforated areas.